3  reaction  +  +  12 C  p process: 14 O+  17 F+p 17 F+p 18 Ne 18 Ne+  … In detail:  p process Alternating ( ,p) and (p,  ) reactions: For each proton capture there is an ( ,p) reaction releasing a proton Net effect: pure He burning

Mass known < 10 keV Mass known > 10 keV Only half-life known seen Measure:  decay properties  gs masses  level properties  rates/cross sections Figure: Schatz&Rehm, Nucl. Phys. A, Reaction rates: direct measurements difficult “indirect” methods: Coulomb breakup (p,p) transfer reactions stable beams and RIBS  Guide direct measurements  Huge reduction in uncertainties  If capture on excited states matters only choice NSCL Set of experiments use (p,d  ) to determine level structure ISOLTRAP Rodriguez et al. NSCL Lebit Bollen et al. ANL CPT Savard et al. Recent progress in mass measurements JYFL Trap

Nuclear physics needed for rp-process: some experimental information available (most rates are still uncertain) Theoretical reaction rate predictions difficult near drip line as single resonances dominate rate: Hauser-Feshbach: not applicable Shell model: available up to A~63 but large uncertainties (often x x10000) (Herndl et al. 1995, Fisker et al. 2001)  Need rare isotope beam experiments  -decay half-lives masses reaction rates mainly (p,  ), ( ,p) (ok) (in progress) (just begun)

Bishop et al (TRIUMF) H. Schatz 1) Direct Measurements For p-capture only 2 cases so far ! 21 Na + p  22 Mg 2) First step: indirect techniques with low intensity rare isotope beams  Need RIA Many developed at a number of facilities: (ANL, GSI, MSU, ORNL, RIKEN, Texas A&M, …) Example: 32 Cl + p  33 Ar*  33 Ar +  Resonant enhancement through states in 33 Ar ? Techniques with rare isotope beams

 -rays from predicted 3.97 MeV state Doppler corrected  -rays in coincidence with 33Ar in S800 focal plane: 33 Ar level energies measured: 3819(4) keV (150 keV below SM) 3456(6) keV (104 keV below SM) 33 Ar level energies measured: 3819(4) keV (150 keV below SM) 3456(6) keV (104 keV below SM) H. Schatz NSCL Experiment: Clement et al. PRL 92 (2004) 2502 x10000 uncertainty shell model only reaction rate (cm 3 /s/mole) temperature (GK) x 3 uncertainty with experimental data stellar reaction rate d Plastic 34Ar 33Ar excited

H. Schatz Stellar Enhancement Factor SEF = stellar capture rate ground state capture rate this work NON Smoker  direct measurement of this rate is not possible – need indirect methods  SEF’s should be calculated with shell model if possible keV Ar 32 Cl 5/2 + 7/2 + 5/2 + 1/2 + MeV Dominant resonance

H. Schatz Mass ejection in X-ray bursts ? Weinberg, Bildsten, Schatz 2005 Temperature (K) Column density (g/cm 2 ) Initial radiative profile wind ? Winds can eject <1% of accreted mass Does convection zone reach into the outer layers that get blown off ???  Wind ejects ashes in radius expansion bursts for wide range of parameters surface Neutron star interior wind depth

H. Schatz Reaction flow during burst rise in pure He flash 12 C 13 N 16 O slow (p,  ) ( ,p) 12 C(  ) bypass Need protons as catalysts (~10  9 are enough !) Source: ( ,p) reactions and feedback through bypass  Increases risetime  Triggers late reexpansion of convection zone  enhances production of heavy elements vs. carbon

H. Schatz Composition of ejected material 32 S 28 Si Weak p-capture on initial Fe seed  Observable with current X-ray telescopes  in wind  on NS surface as spectral edges  Explanation for enhanced Ne/O ratio in 4U , 4U , … ??? (ratios ~1 – ISM 0.18)  Observable with current X-ray telescopes  in wind  on NS surface as spectral edges  Explanation for enhanced Ne/O ratio in 4U , 4U , … ??? (ratios ~1 – ISM 0.18)

Neutron star surface ocean Inner crust outer crust H,He gas ashes ~ 20m,  =10 9 g/cm 3 superburst H. Schatz Step 2: Deep ocean burning: Superbursts

 long duration through longer radiation transport  long time to accumulate means long recurrence time  more material means more total energy by same factor for same MeV/u) Accreting Neutron Star Surface fuel ashes ocean Inner crust outer crust H,He gas core Radiation transport ~1 m ~10 m ~100 m ~1 km 10 km Thermonuclear H+He burning (rp process) ~10s Deep burning ? ~hours ~ x1000 longer burst duration ~ x1000 longer recurrence time ~ x1000 more energy H. Schatz The origin of superbursts – Ashes to Ashes

Burst peak (~7 GK) ~ 45% Energy ~ 55% Energy Carbon can explode deep in ocean (Cumming & Bildsten 2001) (Schatz, Bildsten, Cumming, ApJ Lett. 583(2003)L87 Ashes to ashes – the origin of superbursts ? Puzzle: The ocean is too cold  ignition about every 10 years instead of every year as observed

Energy generation everywhere else in comos: Stars X-ray bursts, Novae Energy generation in Superbursts (plus C->Ni fusion) only place in cosmos ? And nuclear power plants on earth

Neutron star surface ocean Inner crust outer crust H,He gas ashes ~ 25 – 70 m  = g/cm 3 H. Schatz Step 3: Crust burning

Surface of accreting neutron stars Neutron star surface Ocean (palladium? Zinc?) Inner crust Crust of rare isotopes gas D. Page X-ray bursts 1m 10m Hydrogen, Helium ashes

superbursts 34 Ne 1.5 x g/cm 3 68 Ca 1.8 x g/cm Ge 56 Ar 2.5 x g/cm x g/cm 3 72 Ca 4.4 x g/cm 3 rp-ashes 106 Pd 56 Fe Haensel & Zdunik 1990, 2003 Gupta et al Known mass Crust processes

Known mass Crust processes Reach of next generation Rare Isotope Facility FRIB (here MSU’s ISF concept) (mass measurements) Recent mass measurements at GSI (Scheidenberger et al., Matos et al.) Recent mass measurements at GSI (Scheidenberger et al., Matos et al.) Recent TOF mass measurements at MSU (Matos et al.) Recent TOF mass measurements at MSU (Matos et al.) Recent mass measurements at ISOLTRAP (Blaum et. al.) Recent mass measurements at ISOLTRAP (Blaum et. al.) Q-value measurement at ORNL (Thomas et al. 2005) Q-value measurement at ORNL (Thomas et al. 2005) Recent mass measurements at Jyvaskyla (Hager et. al. 2006) Recent mass measurements at Jyvaskyla (Hager et. al. 2006)

Excitation energy of main transition NEW JINA Result: S. Gupta, E. Brown, H. Schatz, K.-L. Kratz, P. Moeller 2007 Electron capture into excited states increases heating by up to a factor of ~10 NEW JINA Result: S. Gupta, E. Brown, H. Schatz, K.-L. Kratz, P. Moeller 2007 Electron capture into excited states increases heating by up to a factor of ~10 Increased heating superbursts rp-ashes

Former estimate New heating enhanced by x 5-6  Heats entire crust and increases ocean temperature from 480 Mio K to 500 Mio K Enhanced crust heating

Impact of new crust modeling on superbursts Can the additional heating from EC into excited states make the crust hot enough to get the superburst ignition depth in line with observations ? Almost: Without excited states Ignition depth Mass number of crust composition (pure single species crust) Inferred from observations

KS (Wijands 2001) Bright X-ray burster for ~12 yr Accretion shut off early 2001 Is residual luminosity cooling neutron star crust ?  If yes: probe neutron star ! H. Schatz Observables: transients in quiescence Low crust conductivity, normal core cooling High crust conductivity, enhanced core cooling (Ouellette & Brown 2005) (Rutledge 2002)

H. Schatz Comparison with observations during quiescence High crust conductivity Enhanced core cooling Low crust conductivity Normal core cooling Low crust conductivity Enhanced core cooling High crust conductivity Normal core cooling (data from Wijnands 2004)  but: a superburst has been observed from KS this indicates a hotter crust and low crust conductivity (Brown 2004) M. Ouellette

H. Schatz Superbursts as probes for NS cooling Superburst ignition depth (Ed Brown, to be published) (for accretion rate of 3e17 g/s and X(12C)=0.1)  Recurrence time depends on crust conductivity and core cooling  Observations require LOW conductivity and no enhanced cooling (incl. KS )  Recurrence time depends on crust conductivity and core cooling  Observations require LOW conductivity and no enhanced cooling (incl. KS ) “regular” core cooling “enhanced” core cooling Low crust conductivity High crust conductivity 27 yr 5.2 yr 1.4 yr 3.1 yr Recurrence times (observed ~ 1yr)